The chains are at least as reliable as the rest of the engine components. Very few engines are damaged by chain failure attibuted to the wear factor ( I have never encountered one), but whenever an overhaul becomes necessary the chains and sprockets, along with most other moving parts, should be renewed.
Hey James,
Do you have an XK powered car or the X300? You might want to post this in the X300 area if you are referring to your 1995 6 cylinder. The Xk engine only has two timing chains.
Cheers Tom